In a case where you think you have done the correct setup for the incoming and outgoing e-mail in the Microsoft Dynamics CRM E-mail Router, yet something isn’t working as expected (e.g. e-mail not sent or tracked correctly), or to troubleshoot any related issues, then you might need to enable tracing.
This Microsoft Support article describes how to enable tracing in Microsoft Dynamics CRM. Scroll down and look for Microsoft Dynamics CRM E-mail Router:
Once enabled, you’ll see very verbose messages, such as:
01/23/2012 15:45:17 : #26090 - An error occurred while opening mailbox firstname.lastname@example.org. System.Net.Sockets.SocketException (0x80004005): No connection could be made because the target machine actively refused it 18.104.22.168:110 at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.Sockets.Socket.Connect(EndPoint remoteEP) at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP) at System.Net.Sockets.TcpClient.Connect(IPAddress address, Int32 port) at Microsoft.Crm.Tools.Email.Providers.Pop3Client.Connect(Boolean useSsl) at Microsoft.Crm.Tools.Email.Providers.Pop3PollingMailboxProvider.OpenMailbox() at Microsoft.Crm.Tools.Email.Providers.CrmPollingMailboxProvider.Run()